1. Field of the Invention
This invention relates to a cathode ray tube device for a projection apparatus for projecting an image on a screen. More particularly, it relates to a cathode ray tube device for a projection apparatus in which a supporting frame for supporting a front panel section of a cathode ray tube and a lens plate mounting a projection lens system are supported by a positioning supporting member detachably mounted on a mounting base plate of the projection apparatus.
2. Description of the Prior Art
There has hitherto been proposed a projection apparatus for putting an image by a cathode ray tube and projecting the image via a projection lens system on a screen. With such projection apparatus, since the image put on the front panel section of the cathode ray tube is projected after being enlarged by the projection lens system, an image of a size larger than that put on the front panel section of the cathode ray tube may be easily projected on the screen.
Meanwhile, the number of pixels put on the cathode ray tube is fixed by a conversion system etc. of image signals supplied to the cathode ray tube. If a color image is to be displayed by the cathode ray tube, it is necessary to display blue-colored component images, green-colored component images and red-colored component images of the color image, each by one-third of the total number of pixels, so that the number of the pixels for displaying the color component images is necessarily decreased.
For this reason, if a color image is to be displayed on the above-described projection apparatus, a first cathode ray tube 101B for displaying a blue-color component image of the color image, a second cathode ray tube 101G for displaying a green-color component image of the color image and a third cathode ray tube 101R for displaying a red-color component image of the color image, as shown in FIG. 1, are employed for increasing the number of pixels for displaying the color component images of the color image for producing a satisfactory image. These cathode ray tubes 101B, 101G and 101R are arrayed horizontally in a side-by-side relation. These cathode ray tubes 101B, 101G and 101R are attached to and supported by a mounting base plate 103 of the projection apparatus by supporting members 105B, 105G and 105R, respectively.
The images of the color components displayed on these cathode ray tubes 101B, 101G, 101R are projected on a screen 102 by means of projection lenses 100, 100, 100 supported on the supporting members 105B, 105G, 105R for facing the front panel section of each of the cathode ray tubes. The color component images of the color image projected on the screen 102 are superimposed one on others to form the color image.
With the projection apparatus for projecting the color image using the first to third cathode ray tubes 101B, 101G, 101R, the projection lenses 100, 100, 100 associated with the cathode ray tubes 101B, 101G, 101R are arranged so that the optical axes of the projection lenses 100, 100, 100 intersect at the center of the screen 102. That is, the optical axes of the projection lenses, 100, 100 associated with the first and third cathode ray tubes 101B and 101R make a convergence angle of .theta..sub.c with respect to a normal to the screen 102, as shown in FIG. l.
With the present projection apparatus, the distance between the rear ends of the projection lenses 100, 100, 100 and the front panel sections of the cathode ray tubes 101B, 101G, 101R associated with these projection lenses, that is the back focal length as shown by an arrow B in FIG. 1 , are set i n dependence upon the distance between the screen 102 and the projection lenses 100.
With the present projection apparatus, the optical axes of the projection lenses 100 and the normal lines to the front panel sections of the cathode ray tubes 101B, 101G, 101R associated with these projection lenses make an elevation, shown by arrow .theta..sub.H shown in FIG. 1 , conforming to the above-mentioned convergence angle.
The convergence angle, elevation and the back focal length are set by the cathode ray tubes 101B, 101G, 101R and the projection lenses 100, 100, 100 being positioned with respect to the mounting base plate 103 by the supporting members 105B, 105G and 105R.
There has also hitherto been proposed a cathode ray tube device for a projector apparatus in which a supporting frame 120 is attached to the front panel section of the cathode ray tube 101 and the angle between the supporting frame 120 and the lens plate 130 carrying the supporting frame 120 and the projection lens is variably adjusted for enabling variable adjustment of the elevation, as shown in FIG. 2. With this conventional cathode ray tube device for the projection apparatus, the lens plate 130 is in the shape of a frame to which is attached an entrance lens 108 which is the last lens of the projection lens system. A lens barrel, not shown, supporting plural lenses of the projection lens system other than the entrance lens 108, is detachably attached to the lens plate 130.
Between the supporting frame 120 and the lens plate 130, a plurality of adjustment supporting members 110 are interposed for supporting the lens plate 130 in a manner of permitting position adjustment with respect to the supporting frame 120. The adjustment supporting members 110 are made up of a first bolt 113 provided upright on a rear surface of the lens plate 130, a second bolt 114 provided upright on the front surface of the supporting frame 120 for facing the first bolt 113 and a turnbuckle member 112 having first and second tapped holes 115, 116 for interconnecting these bolts 113, 114, as shown for example in FIG. 3. With the adjustment supporting member 110, the amounts of threaded engagement between the bolts 113, 114 with the tapped holes 115, 116 are changed on rotation of the turnbuckle member 112 for changing the distance between the supporting frame 120 and the lens plate 130.
With the present cathode ray tube device for the projection apparatus, by adjusting the adjustment supporting members 110 for changing the distance between the supporting frame 120 and the lens plate 130, the angle the supporting frame 120 makes with the lens plate 130 may be adjusted for adjusting the back focal length shown by arrow B in FIG. 2 and the elevation shown by arrow .theta..sub.H in FIG. 2.
Meanwhile, in the projection apparatus in which the cathode ray tubes 101B, 101G, 101R and the projection lenses 100, 100, 100 are positioned by the supporting members 105B, 105G, 105R, the distance between the projection apparatus and the screen 102, that is the distance of projection, is fixed and cannot be changed because it is necessary to change the convergence angle and the elevation in order to change the projection distance.
Meanwhile, for changing the projection distance without changing the convergence angle or the elevation, it may be contemplated to change the distance between the cathode ray tubes 101B, 101G, 101R shown by arrow P in FIG. l. However, in order for the distance between the cathode ray tubes 101B, 101G, 101R to be changed, the projection apparatus must be complicated in construction, because the cathode ray tube needs to be mounted so that its attachment position with respect to the mounting base plate 103 may be changed.
On the other hand, with the projection apparatus employing the cathode ray tube device provided with the adjustment supporting members 110, it is difficult and complex to adjust the back focal length and the elevation correctly. With this conventional projection apparatus, the convergence angle can only be adjusted by tilting the cathode ray tube device for the projection apparatus in its entirety with respect to the mounting base plate of the projection apparatus, such that difficulties are presented if the adjustment is to be performed smoothly and accurately.